Missing skin

I don't expect anyone to believe this, but I got gifted the skin Lord Mordekaiser about 4 months ago and it doesn't show up anymore. I used it once or twice a few days after a stranger gifted it to me after a bot match we played together. I decided to use Mordekaiser today, but my skin doesn't show up. It shows him alongside all of the other skins I don't own. I checked the "skins" page in the shop, and it shows up as a skin I haven't bought yet. I guess I won't die if I don't get it back cause I don't really use Mordekaiser, but just thought that Riot should know that something odd is going on.

Also, while rather irrelevant, I was gifted a mystery skin by a friend a couple days before that (it was Bilgewater Katarina), and it still says I own it.

I guess I can't really provide proof because I got gifted Lord Mordekaiser months ago and it doesn't show up in gifting history.